Study of Itinerant Electron Magnetism on Amorphous (Hf, Ta)Fe_2 Alloys

六方Laves相伪二元金属间化合物(Hf，Ta)Fe2合金表现出两个阶段的磁相变：随着温度的降低，呈现准反铁磁性。我们对高速直流溅射制备的非晶态(Hf，Ta)Fe_2合金的磁性进行了详细的研究。测量了磁化强度和穆斯堡尔效应。非晶态合金的铁磁矩和居里温度随Ta含量x的增加而不断减小，且符合Rhodes-Wohlfarth曲线。这是巡游电子铁磁性的典型特征。结果表明，局部铁矩分布不均匀，与局部环境效应有关。用压量法测量了材料的热膨胀系数。在居里温度附近和以下观察到了正的磁体效应。这个震级随着x的增加而减小，当x&gt；=0.7.3时几乎消失。用斩光式交流法测量了比热。在居里温度约为x=&lt；0.3时，测得比热有一个小峰。在10K以下，比热与温度的关系遵循伽马T+βT^3。电子比热的伽马系数比普通金属要大得多，甚至比相同化学成分的晶相还要大。测量了样品的电阻率和磁阻率。电阻率中居里温度以下的增加量符合铁磁矩随Ta浓度和外场隐含参数的普适函数。这些事实表明，电阻率的变化主要是由于导电电子在局域Fe位的磁散射所致。在10K以下，它遵循T^&lt；1/2&gt；定律，并且几乎与x无关。这似乎是由于基本非晶态结构的贡献，将是下一个有趣的课题。

Hexagonal Laves-phase pseudo-binary intermetallic (Hf, Ta)Fe_2 alloys show two-stage magnetic transition : para- antiferro- ferro-magnetism with decreasing temperature. We have made a detailed study of the magnetism on amorphous (Hf, Ta)Fe_2 alloys obtained from high-rate dc sputtering technique.1. The magnetization and Mossbauer effect have been measured. The ferromagnetic moment and Curie temperature of the amorphous alloys continuously decrease with increasing Ta concentration x and well follow the Rhodes-Wohlfarth curve. This is a typical character of the itinerant electron ferromagnetism. The local Fe moment is found to be inhomogeneously distributed depending on the local environment effects.2. The thermal expansion has been measured by using gauge method. A positive magnetovolume effect has been observed near and below the Curie temperature. This magnitude decreases with increasing x and almost disappears for x >= 0.7.3. The specific heat has been measured by using light-chopped ac method. A small peak in the specific heat has been measured at about the Curie temperature for x =< 0.3. Below 10 K the temperature dependence of the specific heat follows gammaT + betaT^3. The coefficient of the electronic specific heat gamma is much larger compared for the common metal and even larger than the crystalline phase with the same chemical composition.4. The resistivity and magnetoresistivity have been measured. The amount increased below the Curie temperature in the resistivity agrees with the universal function of the ferromagnetic moment with the Ta concentration and external field with implicit parameters. These facts suggest that the variation of the resistivity is mainly due to the magnetic scattering of the conduction electron at the local Fe site. Below 10 K it follows T^<1/2> law and is almost independent of x. This seems to be due the contribution from the fundamental amorphous structure and will be a next interesting subject.